1. Field of the Invention
The present invention relates to a semiconductor device which transmits and receives data using radio signals. In addition, the present invention relates to an external communication device which transmits and receives radio signals to/from a semiconductor device. In addition, the present invention relates to a wireless system having a semiconductor device and a communication device.
2. Description of the Related Art
In recent years, a small semiconductor device in which a small IC chip and an antenna for wireless communication are combined (hereinafter referred to as a semiconductor device; and also called an RFID tag, a wireless tag, an ID tag, an RF tag, or a wireless chip) has attracted attention. The semiconductor device can perform noncontact transmission and reception of data, such as writing and reading data, by transmitting or receiving communication signals to/from an external communication device (hereinafter referred to as a communication device; and also called a reader/writer, a controller, or an interrogator).
As an application field of a semiconductor device which transmits and receives data through radio signals, for example, merchandise management in the distribution industry is given. These days merchandise management with a barcode or the like is widespread; however, data cannot be read when there is an interrupting object because data stored in the barcode is optically read. On the other hand, in data transmission and reception without contact through a wireless communication device, since data in a semiconductor device is read wirelessly, it can be read even if there is an interrupting object. Therefore, a promotion of efficiency and a cost reduction in merchandise management are expected. In addition, the semiconductor device is expected to have a broad range of applications such as railway tickets, air tickets, and automatic payment systems (Reference 1: Japanese Published Patent Application No. 2000-149194). A system in which people or objects are distinguished by using a small semiconductor device which transmits and receives data wirelessly is called RFID (radio frequency identification) and it has attracted attention as a fundamental technology in IT society.